Alcohol is a probable risk factor with regard to colorectal neoplasm and is metabolized to the carcinogen acetaldehyde by the genetically polymorphic alcohol dehydrogenase 3 (ADH3) enzyme. We evaluated whether the association between alcohol and colorectal adenomas is modified by ADH3 polymorphism. We recruited 433 cases with adenomatous polyps and 436 polyp-free controls among Caucasians undergoing endoscopy between 1995 and 2000. Frequency and amount of habitual alcohol consumption were assessed by beverage type, using a validated self-administered food frequency questionnaire. All participants provided blood for genotyping of ADH3. Multivariate analyses adjusting for gender, age, and indication for endoscopy showed that alcohol increased the risk of colorectal adenomas among women [odds ratio (OR), 1.8; 95% confidence interval (CI), 1.0-3.2, >/=10 versus <1 drink/week]. Among men, the risk of adenomas was increased only for those consuming > 21 drinks/week (OR, 1.8; 95% CI, 0.9-3.8, compared with men drinking < 1 drink/week). Among subjects in the highest tertile of alcohol consumption, those with the ADH3*1/*1 genotype were at higher risk (OR, 1.8; 95% CI, 1.0-3.1) than those with other ADH3 genotypes (OR, 1.2; 95% CI, 0.7-1.9) when compared with those in the lowest tertile with ADH3*1/*2 or ADH3*2/*2 genotypes. In conclusion, our findings are consistent with results of other studies, suggesting that alcohol consumption elevates the risk of adenomatous colorectal polyps. ADH3 polymorphism may modify the association between alcohol consumption and colorectal adenomas.